Abstract
Polycyclic aromatic hydrocarbons (PAHs) are widespread genotoxic environmental pollutants and potentially pose a health risk to humans. Although the biological and toxicological activities, including metabolism, mutagenicity, and carcinogenicity, of PAHs have been thoroughly studied, their phototoxicity and photo-induced biological activity have not been well examined. We have long been interested in phototoxicity of PAHs and their derivatives induced by irradiation with UV light. In this paper we report the photoirradiation of a series of oxygenated benz[a]anthracene (BA) and 3-methylcholanthene (3-MC) by UVA light in the presence of a lipid, methyl linoleate. The studied PAHs include 2-hydroxy-BA (2-OH-BA), 3-hydroxy-BA (3-OH-BA), 5-hydroxymethyl-BA (5- CH2OH-BA), 7-hydroxymethyl-BA (7-CH2OH-BA), 12-hydroxymethyl-BA (12-CH2OH-BA), 7-hydroxymethyl-12- methyl-BA (7-CH2OH-12-MBA), 5-formyl-BA (5-CHO-BA), BA 5,6-cis-dihydrodiol (BA 5,6-cis-diol), 1-hydroxy-3- methylcholanthene (1-OH-3-MC), 1-keto-3-methylcholanthene (1-keto-3-MC), and 3-MC 1,2-diol. The results indicate that upon photoirradiation by UVA at 7 and 21 J/cm2, respectively all these compounds induced lipid peroxidation and exhibited a relationship between the dose of the light and the level of lipid peroxidation induced. To determine whether or not photoirradiation of these compounds by UVA light produces ROS, an ESR spin-trap technique was employed to provide direct evidence. Photoirradiation of 3-keto-3-MC by UVA (at 389 nm) in the presence of 2,2,6,6-tetramethylpiperidine (TEMP), a specific probe for singlet oxygen, resulted in the formation of TEMPO, indicating that singlet oxygen was generated. These overall results suggest that UVA photoirradiation of oxygenated BA and 3-methylcholanthrene generates singlet oxygen, one of the reactive oxygen species (ROS), which induce lipid peroxidation.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) are a class of carcinogenic environmental contaminants [1,2,3]
The levels of lipid peroxidation induced by oxygenated methylated BA are shown Figure 3, and those by oxygenated 3-MC are shown in Figure 4, respectively
The PAHs that exhibited the lowest induction of lipid peroxidation are 7-CH2OH-BA and 12-CH2OH-BA
Summary
Polycyclic aromatic hydrocarbons (PAHs) are a class of carcinogenic environmental contaminants [1,2,3]. Since PAHs require metabolic activation in order to exert biological activities, including carcinogenicity [2], study of the mechanisms by which PAHs induce tumors in experimental animals has been one of the most extensively investigated areas of chemical carcinogenesis for the past several decades [1,2,3]. Three metabolic activation pathways in vivo have been determined, metabolism into bay-region diolepoxides [1], radical-cation intermediates [4], and ortho-quinones [5]. All these pathways result in binding of the ultimate metabolites with cellular DNA to form DNA adducts leading to cancer formation.
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